Distorted ship’s hull steel panels

[Bill PudneyParticipant @billpudney37759]

The epoxy compound is only used below the waterline. It is purely functional, it reduces hydrodynamic drag and it reduces and homogenises hull generated noise, aesthetics are not a factor.

Attempting to predict the ultimate shape of the hull and rolling the shell plating so that welding induced distortion is eliminated would probably be theoretically possible but almost certainly outside any cost budget.

It wasn't only the non slip floor coatings that burned and gave off toxic fumes, it was mattresses, bedding, even the sailors clothing was polyester so it burned and melted onto the skin. Horrible.

Performance of a modern warship can be fairly spectacular. Again I was told by someone who would know that HMS Broadsword would accelerate from 0 to 30mph faster than a sports car. I always assumed this was an MG Midget type sports car, not a 7 litre AC Cobra type of sports car!! Certainly being on a launch alongside when she did a standing start sprint, was very impressive.

cheers

Bill

[Bill PudneyParticipant @billpudney37759]

Some hours later I have just realised that I had "hydrodynamic", "homogenises" and "aesthetics" all in the same sentence. Obviously I was sleepwalking and snacking on a thesaurus.

apologetically

Bill

[Roger BestParticipant @rogerbest89007]

If Broadswords top speed was only 30 knots, how was its acceleration quite so good??

**LINK**

[Bill PudneyParticipant @billpudney37759]

The MoD when publishing data about HM ships, they can be a little coy about some information. For instance regarding top speed all they say is "…in excess of 30 knots" In Broadswords case it was well in excess of 30 knots.

cheers

Bill

[Bill PudneyParticipant @billpudney37759]

Thank you all for joining the chat. But I still cannot see why, when they build a big Naval ship, the plates (panels?) all appear indented at launch.

>>>> Trust me Norm, it's the welding of the frames and bulkheads and longitudinals to the shell.

Bill kindly explains the welding might pull in the centres, but that seems odd – couldn't they design the ribs to match the planned curvature in all places?

>>>>The primary consideration is what the sea "sees", that is the actual part of the shell that gets wet. Predicting what the shell is going to do post welding, is certainly possible, however, the shell plating is distorting between the frames/bulkheads and longitudinals.

A big ship like a liner with heavy plates has them all rolled to match the curvature; I don't think the same plate distortion is seen. So, are we thinking that the Naval ships are made with much thinner plates, to make a lighter and faster ship, and try as they might they cannot make them neatly curved all over, and have to resort to seven tonnes of epoxy filler?

>>>Some plates are flat others are rolled to shape, it depends on where they are destined for. Once again, the seven tonnes of epoxy is there for hydrodynamic reasons only. The epoxy is applied only below the waterline. Whether or not the below waterline aesthetics are improved or not is irrelevant and as such not a consideration

So why can't thin steel panels be rolled to a correct curve, and welded to the curved bulkheads and ribs, so that it all looks neat? There is something we are not understanding, and that was the whole point of my first question

.>>>The shell plating is rolled to the correct shape, the plating is distorted by the welding. No doubt it would be feasible to go over the entire above waterline area of the shell and carefully heat and dress the distorted panels flat, so the ships side presented a pleasing appearance to the tax paying population. This however might render the ship rather expensive.

My guess is that localised heating and cooling of the skin from the sun leads to expansion that either has to pop in or out, and standard practice says to make them all pop in. I wonder if this is why the same panel distortion is seen in welded locomotive tenders?

>>> The distortion is not caused by the sun.

But, if the panels are flexing in and out with sun heating, how does the seven tonnes of epoxy stay in shape?

>>> The epoxy is only below the waterline. The sun does not cause the shell plating to "pop" in and out.

italically yours

Bill

[norm nortonParticipant @normnorton75434]

Thank you Bill for kindly addressing the points in my ramble.

I will stop my worrying and accept that it is welding distortion, inevitable in large panels tacked to widely spaced frames

And the Royal Navy does not waste taxpayers' money making the hull above the waterline look like a thing of beauty

[ChrisBParticipant @chrisb35596]

If I recall correctly I had seen an episode of Extreme engineering about the construction of a US carrier where the hull was dressed with sledgehammers.

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